A snap shackle such as is used on a sailboat has a shackle body provided on one side with an eye to which one object--a trapeze harness, jib luff, sheet, halyard, or the like--is attached and another side forming an openable eye to which another object--a deck or mast eye, another line, or the like--is attached. Normally this openable eye is formed between a pair of arms, one of which is unitarily formed with the shackle body and the other of which can pivot between an open and closed position. Latching mechanism is provided on the shackle body for securing the pivotal arm to it when in the closed position.
The most common snap shackle has a spring-loaded pin displaceable in the shackle body in a direction transverse to the plane of the openable eye. The pivotal arm of the openable eye is formed at its free end with a hole that can interfit with the end of this pin to hold this eye closed. When the pin is moved against the force of its spring it leaves the hole in the pivotal arm and releases it to pivot back to the open position.
A common problem with such snap shackles is opening them under load. Frequently the pivotal arm is J-shaped, with the end of its short leg pivoted on the outer end of the fixed arm formed on the shackle body, and the locking mechanism engaging the end of its long leg. Thus even when open such a shackle can remain hooked on the object it is secured to. This can be particularly hazardous when connected to a trapeze harness, as a submerged user can be held under the water by his equipment even after the shackle is opened. Similarly such devices frequently require an inordinate amount of force to open them when heavily loaded, as a component of the force being exerted through the shackle is effective on the opening mechanism in a direction making it difficult to actuate.
Finally it is usual that such shackles are very expensive, particularly due to the high cost of bronze or stainless steel from which they are made and the complexity of the opening mechanism. The machining of the shackle body that receives the piston-type or button-type opener is an expensive procedure that considerably elevates the cost of the fitting. When a plurality of snap shackles are provided along the luff of a jib to secure it to the respective stay, the expense can be vey great.